The invention relates generally to portable circular saws having riving knives positioned in a rearward aft location relative to the cutting blade and adapted to extend into the saw kerf. Such riving knives are configured to substantially prevent the severed portions of the cut workpiece from moving toward one another and pinching the blade, thus creating undesirable drag on the saw blade. More particularly, the present invention relates to a drive mechanism for a movable riving knife that maintains a constant angular orientation or radial clearance relative to the saw blade, and a constant depth projection relative to the saw blade, regardless of the adjusted depth of cut of the saw blade. Preferably, the fore-and-aft location of the riving knife and the distance between the lower, free end of the riving knife and a lower tangent of the cutting blade parallel to the guide shoe are also maintained, regardless of the depth of cut setting. In particular, the present invention is especially adapted for applications in portable circular saws having a rear-pivoting motor-and-gear cases.
Riving knives, which are also sometimes called "splitters", have been provided in a variety of sawing or cutting apparatuses in order to keep the kerf open between severed portions of a workpiece, thereby substantially preventing the kerf from closing and allowing the workpiece portions to pinch the cutting blade. Such riving knife applications have included stationary and portable circular saws.
In the portable circular saw applications, precise control of the riving knife position has frequently presented a problem in that the angular orientation and fore-and-aft location have been difficult to control in response to depth-of-cut adjustments of the saw blade relative to the guide shoe. In order to overcome these problems, various mechanisms, including four-bar linkages, sometimes called "parallelogram linkage arrangements", have been provided in order to impart the desired relative motion to the riving knife to maintain the orientation of the riving knife relatively constant during depth-of-cut adjustment.
Such four-bar linkage arrangements for riving knife drive mechanisms in portable circular saws have suffered the disadvantage of being non-linear in terms of their response to depth-of-cut adjustments, thus making precise control of the riving knife position and orientation difficult. They have also been found to introduce unacceptable "play" into the riving knife motion, due to the tolerances required for relative motion of the various linkage members in such four-bar linkage arrangements. Such previous mechanisms also frequently involve an inordinately large number of parts, thus complicating the manufacture, assembly, and operation of the mechanisms, as well as not being sturdy enough to withstand the rough treatment to which such portable circular saws are frequently subjected in construction operations.
Therefore, some of the objects of the present invention include providing a riving knife drive mechanism capable of relatively linear, precise control of the riving knife position and orientation in response to cutting depth adjustment, a sturdier and more rigid riving knife drive mechanism, when compared to traditional four-bar linkage arrangements, a smoother-acting riving knife drive mechanism, and a relatively simple drive mechanism having a relatively low number of parts, thus facilitating the ease and economy of manufacture, assembly, and operation of the mechanism.
According to the present invention, a portable circular saw includes a guide shoe having a forward or fore end and a rear or aft end, and a motor-and-gear case disposed on one side of the guide shoe, with a transverse output spindle on the motor-and-gear case for supporting a cutting blade in a fore-and-aft cutting plane. The motor-and-gear case is pivotally supported on the shoe by a rear pivot mechanism for rotation about a transverse rear pivot axis, thus allowing for selective adjustment of the blade cutting depth on the opposite side of the shoe. In such an arrangement, the depth of cut setting is increased and decreased when the motor-and-gear case is rotated relative to the shoe in respective first and second directions, while an upper pivotal blade guard, which is mounted on the motor-and-gear case for rotation about the spindle, rotates in opposite rotational directions in response to respective increases and decreases in the depth of cut setting.
The preferred circular saw also includes a drive link pivotally connected to the guard, preferably at a location between the spindle and the rear pivot mechanism, a riving knife interconnected with the saw for pivotal rotation about the spindle, and cam-and-follower means interconnecting the shoe, the guard, the case, and the riving knife for rotating the guard in the first and second rotational directions when the depth of cut setting is decreased and increased, respectively, and for maintaining the riving knife and the shoe in the same relative angular orientation in the fore-and-aft cutting plane regardless of the depth of cut setting.
In the preferred riving knife drive arrangement, which is discussed in detail below and depicted for purposes of illustration in the drawings, a first cam surface and cam follower mechanism is interconnected between the shoe and the guard for rotating the guard about the spindle in response to depth of cut setting adjustments. A second cam surface and cam follower mechanism is interconnected between the riving knife and the drive link, and a third cam surface and cam follower mechanism is interconnected between the gear case and the drive link. The second and third cam surface and cam follower mechanisms maintain the riving knife in the same orientation relative to the shoe regardless of the depth of cut setting. Preferably, the location of the riving knife in the fore-and-aft direction is also maintained regardless of cutting depth setting, as is the distance between the free end of the riving knife and a lower tangent to the cutting blade.
Additional objects, advantages, and features of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings.